Ground Referenced Current Sensing Circuit for LED Drivers
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Solution Overview
Problem
Driver circuits face challenges in providing a ground referenced signal for current regulation, especially when loads require voltages higher than the input voltage, as traditional resistor-based methods are ineffective and integrated circuit solutions are cost-prohibitive for applications like LED lighting in vehicles.
Innovation Solution
A current sensing circuit comprising a resistive shunt and a current mirror is used to generate a ground referenced output signal, with a bias resistor to minimize voltage variation, allowing the driver circuit to regulate current effectively across varying input voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistor is placed between ground and the negative terminal of the load to provide a ground referenced signal, then the current regulation is accurate, but this method is only effective when the load voltage is less than the input voltage
Solution Approach 1:
The patent introduces a current mirror circuit as an intermediary mechanism that transfers the current information from the load path to a ground-referenced output path. The current mirror consists of multiple transistors that replicate the current flowing through the resistive shunt, allowing the current information to be available at a ground-referenced node without requiring direct connection between the load negative terminal and ground.
Solution Approach 2:
The current mirror creates a copy of the load current through the resistive shunt and presents this copied current information at a ground-referenced output. This allows the control circuit to access accurate current information without requiring the load to be connected in a specific configuration relative to ground.
2Measurement precision
If an integrated circuit solution is used to provide a ground referenced signal proportional to the actual current, then accurate current regulation is achieved, but the cost becomes prohibitive for many applications
Solution Approach 1:
The patent divides the current sensing function into discrete, simple components: a resistive shunt for voltage development and a current mirror implemented with individual transistors and resistors. This segmentation allows the circuit to be built from standard, low-cost components rather than requiring an expensive integrated circuit solution.
Solution Approach 2:
The patent replaces expensive integrated circuit current sensors with inexpensive discrete components including standard transistors and resistors. This substitution dramatically reduces the cost of the current sensing circuit while maintaining the required measurement accuracy for LED driver applications.
3Device complexity
If the load is connected between the positive terminal of the converter and ground to enable simple current sensing, then the circuit complexity is reduced, but the load cannot receive sufficient voltage when the input voltage is insufficient
Solution Approach 1:
The current mirror circuit acts as an intermediary that decouples the power delivery function from the current sensing function. This allows the load to be connected in the optimal position for power delivery (between converter output and negative terminal) while still providing accurate ground-referenced current information to the control circuit.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables accurate and cost-effective regulation of current to loads, such as LEDs, by providing a ground referenced output signal that is independent of input voltage variations, thus optimizing energy delivery and reducing costs.
Implementation Method 1
a current mirror for producing a ground referenced output signal indicative of a current through the resistive shunt
Implementation Method 2
a bias resistor which induces a bias current in the second resistor such that the ground referenced output signal varies little in response to a change in an input voltage of the converter
Data Source
AI summary
A current sensing circuit for sensing the current provided to LEDs by a constant current power source includes a resistive shunt in series with the load and a current mirror having a first leg connected to a first terminal of the resistive shunt and a second leg connected to a second terminal of the resistive shunt. Both legs of the current mirror are also connected to ground. The first leg provides a reference signal to the second leg, and the second log uses the reference signal and a voltage at the second terminal of the resistive shunt to provide a ground referenced output signal indicative of the current provided to the LEDs.